Liquid crystal display device

ABSTRACT

According to one embodiment, a liquid crystal display device includes second substrates, a light-shielding layer, and a liquid crystal layer. The first substrate includes pixel electrodes, a common electrode, and subpixel areas each including area in which the pixel electrode is present and a second area in which the pixel electrode is not present. Each of the subpixel areas includes first and second sides. The first area includes an axial area and branch areas. The second area includes a gap area between the adjacent branch areas. The axial area includes a projection portion projecting to the second side and in alignment with the gap area, and overlaps the light-shielding layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-166440, filed Aug. 29, 2016, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a liquid crystaldisplay device.

BACKGROUND

A liquid crystal display device in in-plane switching (IPS) mode isknown as an example of a display device. The liquid crystal displaydevice in IPS mode comprises a pair of substrates facing each other viaa liquid crystal layer. One of the substrates comprises a pixelelectrode and a common electrode. The alignment of the liquid crystalmolecules of the liquid crystal layer is controlled using the lateralelectric field generated between the electrodes. A liquid crystaldisplay device in fringe-field switching (FFS) mode has been put topractical use. In the liquid crystal display device in FFS mode, a pixelelectrode and a common electrode are provided in different layers, andthe fringe electric field generated between the electrodes is used tocontrol the alignment of liquid crystal molecules.

The following liquid crystal display device has been developed. In theliquid crystal display device, a pixel electrode and a common electrodeare provided in different layers. A slit is provided in the electrodecloser to a liquid crystal layer than the other electrode. The liquidcrystal molecules near the both edges of the slit in the width directionare rotated in opposite directions. The system of this liquid crystaldisplay device is clearly different from the FFS mode, and can increasethe speed of response and improve the stability of alignment incomparison with the conventional FFS mode. Hereinafter, the structure ofthis type of liquid crystal display device is called a high-speedresponse mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the general structure of a liquidcrystal display device according to a first embodiment.

FIG. 2 shows the general equivalent circuit of the liquid crystaldisplay device according to the first embodiment.

FIG. 3 shows a part of a cross-sectional surface of the liquid crystaldisplay device according to the first embodiment.

FIG. 4 is a general plan view of a subpixel provided in the liquidcrystal display device according to the first embodiment.

FIG. 5 is a partial enlarged view of the pixel electrode shown in FIG.4.

FIG. 6 shows the initial alignment state of liquid crystal moleculeswhen no electric field is generated.

FIG. 7 shows the alignment state of liquid crystal molecules when anelectric field is generated.

FIG. 8 shows a comparative example with the present embodiment.

FIG. 9 is a general plan view showing a part of a pixel electrodeaccording to a second embodiment.

FIG. 10 is a general plan view showing a part of a pixel electrodeaccording to a third embodiment.

FIG. 11 is a general plan view showing a part of a pixel electrodeaccording to a fourth embodiment.

FIG. 12 shows a part of a cross-sectional surface of a liquid crystaldisplay device according to a fifth embodiment.

FIG. 13 is a general plan view of a common electrode according to thefifth embodiment.

FIG. 14 is a partial enlarged view of the pixel electrode shown in FIG.13.

DETAILED DESCRIPTION

In general, according to one embodiment, a liquid crystal display devicecomprises a first substrate, a second substrate, a light-shieldinglayer, and a liquid crystal layer including liquid crystal moleculesbetween the first substrate and the second substrate. The firstsubstrate comprises a plurality of video signal lines, pixel electrodeselectrically connected to the video signal lines, a common electrodefacing the pixel electrodes and rotating the liquid crystal molecules bygenerating an electric field between the common electrode and the pixelelectrodes, and a plurality of subpixel areas each comprising a firstarea and a second area. The first area is an area in which the pixelelectrode is present, and the second area is an area in which the pixelelectrode is not present. Each of the subpixel areas comprises a firstside and a second side in a first direction. The first area includes anaxial area extending in a second direction intersecting the firstdirection, and a plurality of branch areas extending in the firstdirection from the axial area to the first side. The second areaincludes a gap area extending in the first direction between theadjacent branch areas. The axial area comprises a projection portionprojecting to the second side and in alignment with the gap area in thefirst direction, and overlaps the light-shielding layer.

According to another embodiment, a liquid crystal display devicecomprises a first substrate, a second substrate, a light-shieldinglayer, and a liquid crystal layer including liquid crystal moleculesbetween the first substrate and the second substrate. The firstsubstrate comprises a plurality of video signal lines, pixel electrodeselectrically connected to the video signal lines, a common electrodefacing the pixel electrodes and rotating the liquid crystal molecules bygenerating an electric field between the common electrode and the pixelelectrodes, and a plurality of subpixel areas each comprising a firstarea and a second area. The first area is an area in which the commonelectrode is not present, and the second area is an area in which thecommon electrode is present. Each of the subpixel areas comprises afirst side and a second side in a first direction. The first areaincludes an axial area extending in a second direction intersecting thefirst direction, and a plurality of branch areas extending in the firstdirection from the axial area to the first side. The second areaincludes a gap area extending in the second direction between theadjacent branch areas. The axial area comprises a projection portionprojecting to the second side and in alignment with the gap area in thefirst direction, and overlaps the light-shielding layer.

The above structures allow the provision of a liquid crystal displaydevice in high-speed response mode in which the stability of alignmenthas been further improved.

Various embodiments will be described with reference to the accompanyingdrawings.

The disclosure is merely an example, and proper changes in keeping withthe spirit of the invention, which are easily conceivable by a person ofordinary skill in the art, come within the scope of the invention as amatter of course. In addition, in some cases, in order to make thedescription clearer, the drawings are schematically illustrated ratherthan as an accurate representation of what is implemented. However, suchschematic illustration is merely exemplary, and in no way restricts theinterpretation of the invention. In the drawings, reference numbers ofcontinuously arranged elements equivalent or similar to each other areomitted in some cases. In the specification and drawings, structuralelements which function in the same or a similar manner to thosedescribed in connection with preceding drawings are denoted by likereference numbers, detailed description thereof being omitted unlessnecessary.

In each embodiment, a transmissive type liquid crystal display device isdisclosed as an example of a liquid crystal display device. However,each embodiment does not prevent application of individual technicalideas disclosed in the embodiment to other types of display devices.Other types of display devices are assumed to include, for example, areflective type liquid crystal display device which displays an imageusing outside light, and a liquid crystal display device having both thetransmissive function and the reflective function.

In this specification, the phrases “α includes A, B or C”, “α includesone of A, B and C” and “α includes an element selected from a groupconsisting of A, B and C” do not exclude a case where α includes aplurality of combinations of A to C unless specified. Further, thesephrases do not exclude a case where α includes other elements.

First Embodiment

FIG. 1 is a perspective view showing the general structure of a liquidcrystal display device 1 (hereinafter, referred to as a display device1) according to a first embodiment. The display device 1 may be used forvarious devices such as a smartphone, a tablet, a mobile phone, acomputer, a television receiver, an in-vehicle unit, a game console anda wearable device.

The display device 1 comprises a display panel 2, a backlight 3 facingthe display panel 2, a driver IC 4 which drives the display panel 2, acontrol module 5 which controls the operation of the display panel 2 andthe backlight 3, and flexible circuit boards FPC1 and FPC2 whichtransmit a control signal to the display panel 2 and the backlight 3.

In the present embodiment, a first direction D1 is the direction ofextension of each branch area 40 as described later. A second directionD2 is the direction of extension of each axial area 30 as describedlater. In FIG. 1, the first direction D1 is also applicable to adirection parallel to the short sides of the display panel 2. The seconddirection D2 is also applicable to, for example, a direction parallel tothe long sides of the display panel 2. In the example shown in FIG. 1,the first direction D1 is perpendicular to the second direction D2.However, the first and second directions D1 and D2 may intersect atanother angle.

The display panel 2 comprises first and second substrates SUB1 and SUB2facing each other, and a liquid crystal layer (the liquid crystal layerLC described later) provided between the first and second substratesSUB1 and SUB2. The display panel 2 comprises a display area DA whichdisplays an image. The display panel 2 comprises, for example, aplurality of pixels PX arranged in matrix in the first and seconddirections Dl and D2 in the display area DA.

FIG. 2 shows the general equivalent circuit of the display device 1. Thedisplay device 1 comprises a first driver DR1, a second driver DR2, aplurality of scanning signal lines G connected to the first driver DR1,and a plurality of video signal lines S connected to the second driverDR2. The scanning signal lines G extend in the first direction D1 andare arranged in the second direction D2 in the display area DA. In thedisplay area DA, the video signal lines S extend in the second directionD2, are arranged in the first direction D1, and intersect the scanningsignal lines G.

The display device 1 comprises a plurality of subpixel areas A. Thesubpixel areas A are defined by the scanning signal lines G and thevideo signal lines S as seen in plan view. A subpixel SP is formed ineach subpixel area A. In the present embodiment, it is assumed that eachpixel PX includes a subpixel SPR displaying red, a subpixel SPGdisplaying green and a subpixel SPB displaying blue. However, each pixelPX may further include, for example, a subpixel SP displaying white, ormay include a plurality of subpixels SP corresponding to the same color.

Each subpixel SP comprises a switching element SW, a pixel electrode PE,and a common electrode CE facing the pixel electrode PE. The commonelectrode CE is formed over a plurality of subpixels SP. Each switchingelement SW is connected to a corresponding scanning signal line G, acorresponding video signal line S and a corresponding pixel electrodePE. Each pixel electrode PE is electrically connected to a correspondingvideo signal line S via a corresponding switching element SW.

The first driver DR1 supplies a scanning signal to the scanning signallines G in series. The second driver DR2 selectively supplies a videosignal to the video signal lines S. When a scanning signal is suppliedto a scanning signal line G corresponding to a switching element SW, andfurther when a video signal is supplied to the video signal line Sconnected to the switching element SW, voltage is applied to the pixelelectrode PE in accordance with the video signal. At this time, anelectric field is generated between the pixel electrode PE and thecommon electrode CE. By this electric field, the alignment of the liquidcrystal molecules of the liquid crystal layer LC is changed from theinitial alignment state where no voltage is applied. By this operation,an image is displayed in the display area DA.

FIG. 3 shows a part of a cross-sectional surface of the display device1. The cross-sectional surface shown in FIG. 3 is the cross-sectionalsurface of subpixels SPR, SPG and SPB included in a pixel PX in thefirst direction D1.

The first substrate SUB1 comprises a first insulating substrate 10 suchas a phototransmissive glass substrate or resin substrate. The firstinsulating substrate 10 comprises a first main surface 10A facing thesecond substrate SUB2, and a second main surface 10B provided on a sideopposite to the first main surface 10A. The first substrate SUB1 furthercomprises the switching elements SW, the pixel electrodes PE, the commonelectrode CE, a first insulating layer 11, a second insulating layer 12and a first alignment film 13.

Each switching element SW is provided on the first main surface 10A ofthe first insulating substrate 10, and is covered with the firstinsulating layer 11. In FIG. 3, the illustration of the scanning signallines G or the video signal lines S is omitted. Moreover, in FIG. 3,each switching element SW is simplified. In the actual device, the firstinsulating layer 11 includes a plurality of layers, and the switchingelements SW include semiconductor layers and various electrodes formedin the layers included in the first insulating layer 11.

In the example of FIG. 3, subpixels SPR, SPG and SPB comprise therespective pixel electrodes PE. The common electrode CE is provided oversubpixels SPR, SPG and SPB. The common electrode CE is formed on thefirst insulating layer 11, and comprises an aperture 14 at a positionfacing each pixel electrode PE. The common electrode CE is covered withthe second insulating layer 12.

The pixel electrodes PE are formed on the second insulating layer 12,and face the common electrode CE. The pixel electrodes PE areelectrically connected to the switching elements SW of subpixels SPR,SPG and SPB via the apertures 14, respectively. The pixel electrodes PEand the common electrode CE may be formed of a transparent conductivematerial such as indium tin oxide (ITO). The first alignment film 13covers the pixel electrodes PE, and is in contact with the liquidcrystal layer LC.

The second substrate SUB2 comprises a second insulating substrate 20such as a phototransmissive grass substrate or resin substrate. Thesecond insulating substrate 20 comprises a first main surface 20A facingthe first substrate SUB1, and a second main surface 20B provided on aside opposite to the first main surface 20A. The second substrate SUB2further comprises color filters 21 (21R, 21G and 21B), a light-shieldinglayer 22, an overcoat layer 23 and a second alignment film 24. Thelight-shielding layer 22 may be provided in the first substrate SUB1.

As seen in plan view, the light-shielding layer 22 is provided in eachboundary between subpixels SPR, SPG and SPB. The overcoat layer 23covers color filters 21R, 21G and 21B, and planarizes the surfaces ofcolor filters 21R, 21G and 21B. The second alignment film 24 covers theovercoat layer 23, and is in contact with the liquid crystal layer LC.

Thus, the first alignment film 13 and the second alignment film 24 havea function for causing the liquid crystal molecules contained in theliquid crystal layer LC to align in the initial alignment direction. Forexample, the first alignment film 13 and the second alignment film 24are optical alignment films obtained by optical alignment treatment forirradiating polymer films such as polyimide with ultraviolet so as toimpart anisotropy. However, the first alignment film 13 and the secondalignment film 24 may be rubbing alignment films obtained by rubbingtreatment. Alternatively, one of the first alignment film 13 and thesecond alignment film 24 may be an optical alignment film, and the otherone may be a rubbing alignment film.

In the example of FIG. 3, a first optical element OD1 including a firstpolarizer PL1 is provided on the second main surface 10B of the firstinsulating substrate 10. A second optical element OD2 including a secondpolarizer PL2 is provided on the second main surface 20B of the secondinsulating substrate 20.

FIG. 4 is a plan view schematically showing an example of a subpixel SP.Each of the above subpixel areas A is surrounded by two scanning signallines G adjacent to each other in the second direction D2 and two videosignal lines S adjacent to each other in the first direction D1. Thesubpixel area A comprises a first side SD1 (the right side in thefigure) and a second side SD2 (the left side in the figure) in the firstdirection D1.

The subpixel area A comprises a first area Al and a second area A2. InFIG. 4, the first area A1 is indicated with a dot pattern. The secondarea A2 has a shape obtained by removing the first area A1 from thesubpixel area A.

The first area A1 comprises the axial area 30, and a plurality of branchareas 40. The axial area 30 extends in the second direction D2, and isarranged on the second side SD2 in the subpixel area A. Each branch area40 extends from the axial area 30 to the first side SD1 in the firstdirection D1. For example, each branch area 40 has a shape taperingtoward an end.

In FIG. 4, the first area A1 further comprises an end area 50. The endarea 50 extends from the axial area 30 to the first side SD1 in thefirst direction D1 in a manner similar to that of the branch areas 40.The end area 50 has a width greater than that of each branch area 40 inthe second direction D2.

The second area A2 comprises a gap area 60 extending in the firstdirection D1 between two branch areas 40 adjacent to each other in thesecond direction D2. In addition, the gap area 60 is formed between theend area 50 and the branch area 40 adjacent to the end area 50.

In the example of FIG. 4, all of the branch areas 40 have the sameshape, and are arranged in the second direction D2 at regular intervals.Similarly, all of the gap areas 60 have the same shape, and are arrangedin the second direction D2 at regular intervals. However, the shapes orintervals of the branch areas 40 or the gap areas 60 are not necessarilythe same as each other. The shapes or intervals may be partiallydifferent from each other.

In one of the first and second areas A1 and A2, the pixel electrode PEis present. In the other one, pixel electrode PE is not present. In theexample of FIG. 4, the pixel electrode PE is formed in the first areaA1, and no pixel electrode PE is formed in the second area A2. In thepresent embodiment, the shape of the first area A1 is equivalent to theshape of the pixel electrode PE.

The switching element SW comprises a semiconductor layer SC. Thesemiconductor layer SC is connected to the video signal line S at aconnective position P1, and is connected to the pixel electrode PE at aconnective position P2. In the example of FIG. 4, connective position P2is included in the end area 50. The semiconductor layer SC intersectsthe upper scanning signal line G in the figure twice. Thus,

FIG. 4 shows an example in which the switching element SW is adouble-gate switching element. However, the switching element SW may bea single-gate switching element which intersects the scanning signalline G only once.

In FIG. 4, the border portions of the light-shielding layer 22 are shownwith alternate long and short dash lines. The light-shielding layer 22overlaps the scanning signal lines G, the video signal lines S and theswitching element SW. Moreover, in the example of FIG. 4, thelight-shielding layer 22 overlaps the entire part of the axial area 30,and overlaps the proximal ends (the vicinity of the positions connectedto the axial area 30) and distal ends of the branch areas 40. Thelight-shielding layer 22 may not overlap a part of the axial area 30.The light-shielding layer 22 may not overlap the proximal ends or distalends of the branch areas 40.

Alignment treatment is applied to the first alignment film 13 and thesecond alignment film 24 shown in FIG. 3 in an alignment treatmentdirection AD parallel to the first direction D1. Thus, the firstalignment film 13 and the second alignment film 24 have a function forcausing the liquid crystal molecules to align in the initial alignmentdirection parallel to the alignment treatment direction AD. In thepresent embodiment, the direction of extension of the branch areas 40conforms to the initial alignment direction of the liquid crystalmolecules.

Now, this specification explains the details of the shape of the pixelelectrode PE (the first area A1). FIG. 5 is a partial enlarged view ofthe pixel electrode PE shown in FIG. 4. Each branch area 40 comprises afirst edge 41 and a second edge 42 in the second direction D2. Eachbranch area 40 further comprises a top edge 43 connecting the first edge41 and the second edge 42 at the distal end. The axial area 30 comprisesa bottom edge 31 between two adjacent branch areas 40. Each first edge41 is inclined by an angle θ (for example, approximately 1 degree) whichis an acute angle in a clockwise direction with respect to the alignmenttreatment direction AD. Each second edge 42 is inclined by the angle θin a counterclockwise direction with respect to the alignment treatmentdirection AD.

A corner C1 is formed by the bottom edge 31 and the first edge 41. Acorner C2 is formed by the first edge 41 and the top edge 43. A cornerC3 is formed by the bottom edge 31 and the second edge 42. A corner C4is formed by the second edge 42 and the top edge 43.

The axial area 30 comprises connective areas 33 connected to the branchareas 40, and non-connective areas 34 adjacent to the gap areas 60 inthe first direction D1. The connective areas 33 and the non-connectiveareas 34 are alternately arranged in the second direction D2.

The axial area 30 comprises an edge 32 on a side opposite to the bottomedges 31. The edge 32 corresponds to a side of the axial area 30 on thesecond side SD2. The edge 32 comprises a flat portion 101 provided ineach non-connective area 34, and inclined portions 102 and 103 providedin each connective area 33. The flat portion 101 and inclined portions102 and 103 are repeatedly formed in this order in the second directionD2. Each flat portion 101 extends parallel to the second direction D2.Inclined portions 102 and 103 extend in directions intersecting thefirst and second directions D1 and D2.

By the flat portions 101 and inclined portions 102 and 103, projectionportions 35 projecting to the second side SD2 and concave portions 36depressed to the first side SD1 are alternately formed. Each projectionportion 35 is in alignment with a corresponding gap area 60 in the firstdirection D1. Each concave portion 36 is in alignment with acorresponding branch area 40 in the first direction D1. In the exampleof FIG. 5, the concave portions 36 are provided in the connective areas33. The projection portions 35 are equivalent to portions betweenadjacent concave portions 36, in other words, the non-connective areas34. For example, as shown in FIG. 5, each concave portion 36 is atriangle comprising inclined portions 102 and 103 in plan view. In planview, each projection portion 35 is a trapezoid comprising the flatportion 101 and inclined portions 102 and 103. The shapes of the concaveportions 36 or the projection portions 35 are not limited to thisexample. For example, each concave portion 36 may be trapezoidal, andeach projection portion 35 may be triangular.

Bend portions BP1 and BP2 are formed at the borders between eachconnective area 33 and the two non-connective areas 34 provided aboveand under the connective area 33 (or the borders between each concaveportion 36 and the projection portions 35). In the example of FIG. 5,each bend portion BP1 comprises the flat portion 101 and inclinedportion 102. Each bend portion BP2 comprises the flat portion 101 andinclined portion 103. For example, bend portions BP1 and BP2 arepreferably extensions of the first and second edges 41 and 42 of eachbranch area 40, respectively.

The length of each connective area 33 in the second direction D2 is L1.The length of each non-connective area 34 in the second direction D2 isL2. Length L2 is preferably greater than length L1 (L2>L1). However,length L2 may be less than or equal to length L1 (L2≤L1).

The length (height) of each projection portion 35 in the first directionD1 is L3. Length L3 is equivalent to the length (depth) of each concaveportion 36 in the first direction D1. The length (width) of eachnon-connective area 34 in the first direction D1 is L4. The maximumlength of each connective area 33 in the first direction D1 is also L4.For example, length L3 is preferably greater than or equal to 1 μm.Length L3 is preferably greater than or equal to one-third of length L4.

The length of each branch area 40 in the first direction D1 is L5. Eachbranch area 40 is an area substantially contributing to display. Asdescribed above, the axial area 30 overlaps the light-shielding layer22. Thus, when length L3 of each projection portion 35 is excessivelygreat in comparison with length L5 of each branch area 40, an area whichdoes not contribute to display is large. Thus, the display quality isdegraded. In this respect, length L4 of each non-connective area 34 inthe first direction D1 is preferably less than or equal to one-fifth ofthe total width (L4+L5) of the connective area 33 and the branch area 40in the first direction D1.

The projection portions 35 or the concave portions 36 are not limited tothe example shown in FIG. 5. They may be modified in various ways suchas the shapes of the second to fourth embodiments described later.

The shape of the pixel electrodes PE of the present embodiment allowsthe realization of a high-speed response mode in which the response isfaster than that of the common FFS mode. The speed of response can bedefined as, for example, the speed when the light transmittance of theliquid crystal layer LC is changed between predetermined levels by thevoltage application between the pixel electrodes PE and the commonelectrode CE.

Now, this specification explains the operation principle of thehigh-speed response mode with reference to FIG. 6 and FIG. 7.

FIG. 6 shows a part of the pixel electrode PE (the first area A1), andthe initial alignment state of the liquid crystal molecules LM containedin the liquid crystal layer LC. As shown in FIG. 6, the liquid crystalmolecules LM are initially aligned such that the long axis conforms tothe alignment treatment direction AD in an off-state where no voltage isapplied between the pixel electrode PE and the common electrode CE.

In the common FFS mode which is widely used, all the liquid crystalmolecules rotate in the same direction when a fringe electric field isformed between two electrodes. However, the rotation of the liquidcrystal molecules in high-speed response mode is different from that ofthe liquid crystal molecules in FFS mode.

FIG. 7 shows the alignment state of the liquid crystal molecules LM inan on-state where voltage is applied between the pixel electrode PE andthe common electrode CE. Lines EL1 and EL2 shown in FIG. 7 are examplesof equipotential lines of the electric field generated around the pixelelectrode PE. In the liquid crystal molecules LM of the presentembodiment, the dielectric anisotropy is positive. Therefore, whenvoltage is applied between the pixel electrode PE and the commonelectrode CE in the off-state shown in FIG. 6, force is applied torotate the liquid crystal molecules LM such that the long axis is madeparallel to the direction of the electric field generated by theapplication of voltage (or is made perpendicular to equipotential linesEL1 and EL2).

The liquid crystal molecules LM rotate in a first rotational directionR1 indicated with the solid arrows near corners C1 and C2. The liquidcrystal molecules LM rotate in a second rotational direction R2indicated with the dashed arrows near corners C3 and C4. The firstrotational direction R1 and the second rotational direction R2 aredirections different from each other (in other words, rotationaldirections opposite to each other).

Corners C1 to C4 have a function for controlling the alignment (in otherwords, a function for stabilizing the alignment) by controlling therotational direction of the liquid crystal molecules LM near the firstand second edges 41 and 42. The liquid crystal molecules LM near thefirst edges 41 rotate in the first rotational direction R1 in connectionwith the rotation of the liquid crystal molecules LM near corners C1 andC2. The liquid crystal molecules LM near the second edges 42 rotate inthe second rotational direction R2 in connection with the rotation ofthe liquid crystal molecules LM near corners C3 and C4. Near the centerof each branch area 40 and the center of each gap area 60 in the seconddirection D2, the liquid crystal molecules LM rotating in the firstrotational direction R1 compete with the liquid crystal molecules LMrotating in the second rotational direction R2. The liquid crystalmolecules LM in these areas are maintained in the initial alignmentstate, and hardly rotate.

As described above, in high-speed response mode, the rotationaldirections of the liquid crystal molecules LM are aligned from theproximal ends to the distal ends near the first and second edges 41 and42. Thus, when voltage is applied, a response can be made fast.Moreover, the rotational directions of the liquid crystal molecules LMcan be uniform. Thus, it is possible to improve the stability ofalignment.

In the branch areas 40, the first and second edges 41 and 42 areinclined with respect to the alignment treatment direction AD. Thisstructure also contributes to the improvement of the stability ofalignment. Near the first and second edges 41 and 42 inclined withrespect to the alignment treatment direction AD, the direction of theelectric field intersects the alignment treatment direction AD at anangle other than a right angle. Thus, it is possible to cause therotational direction of the liquid crystal molecules LM to besubstantially constant when voltage is applied.

Now, this specification particularly looks at the vicinity of the edge32 of the axial area 30. As described above, the edge 32 comprises theprojection portions 35 and the concave portions 36. Equipotential lineEL2 meanders in line with the shapes of the projection portions 35 andthe concave portions 36. From bend portions BP1 and BP2 to the center ofthe concave portion 36 in the second direction D2, equipotential lineEL2 inclines in directions intersecting the first and second directionsD1 and D2. In this way, near bend portions BP1, the liquid crystalmolecules LM rotate in the first rotational direction R1. Near bendportions PB2, the liquid crystal molecules LM rotate in the secondrotational direction R2. Near the center of each concave portion 36 andthe center of each projection area 35 in the second direction D2, theliquid crystal molecules LM rotating in the first rotational directionR1 compete with the liquid crystal molecules LM rotating in the secondrotational direction R2. The liquid crystal molecules LM in these areasare maintained in the initial alignment state, and hardly rotate.

When the liquid crystal molecules LM near the edge 32 rotate as describeabove, as surrounded by dashed frames, the rotational directions of theliquid crystal molecules LM are aligned from the first edge 41 to bendportion BP1, and further, the rotational directions of the liquidcrystal molecules LM are aligned from the second line 42 to bend portionBP2. From the branch areas 40 to the concave portions 36, the liquidcrystal molecules LM do not rotate in the centers of the branch areas 40or the concave portions 36 in the second direction D2. Similarly, fromthe gap areas 60 to the projection portions 35, the liquid crystalmolecules LM do not rotate in the centers of the gap areas 60 or theprojection portions 35 in the second direction D2.

A comparison example with the present embodiment is shown in FIG. 8. Thecomparison example assumes that the edge 32 of the axial area 30 is flatin the second direction D2. In this case, equipotential line EL2 isparallel to the second direction D2 over the entire edge 32. Sinceequipotential line EL2 is perpendicular to the alignment treatmentdirection AD, the liquid crystal molecules LM near the edge 32 mayrotate in either the first rotational direction R1 or the secondrotational direction R2. Thus, the state is unstable. For example, in acase of pixels with high-definition, the electrodes are small. Thus, thefirst and second rotational directions R1 and R2 of the liquid crystalmolecules LM near the edge 32 more easily become unstable. For example,when the length of the axial area (in FIG. 5, each non-connective area34) is less than or equal to 3.5 μm, or less than or equal to 3 μm, theabove unstable rotation more easily occurs.

When the liquid crystal molecules LM near the extension of the firstedge 41 rotate in the second rotational direction R2, the rotationaldirection of the liquid crystal molecules near the first edge 41 is notaligned with that near the edge 32. Similarly, when the liquid crystalmolecules LM near the extension of the second edge 42 rotate in thefirst rotational direction R1, the rotational direction of the liquidcrystal molecules near the second edge 42 is not aligned with that nearthe edge 32. When the rotational directions are not aligned with eachother in this way, the speed of response is slow near the first andsecond edges 41 and 42.

When equipotential line LE2 is bent as shown in FIG. 7 by providing theprojection portions 35 or the concave portions 36 in the edge 32, therotational directions of the liquid crystal molecules LM near the edge32 are aligned with those near the first and second edges 41 and 42. Inthis way, the speed of response in high-speed response mode can befurther increased.

By increasing the speed of response, the image displayed on the displaydevice 1 is quickly switched. Thus, various preferable effects can beobtained. For example, an image can be displayed with high quality.

The shape of each pixel electrode PE (first area A1) is not limited tothe example disclosed in the present embodiment. Modification examplesof the shape of each pixel electrode PE are shown in the followingsecond to fifth embodiments.

Second Embodiment

FIG. 9 is a general plan view showing a part of a pixel electrode PEaccording to the second embodiment. In the pixel electrode PE shown inFIG. 9, an edge 32 provided in an axial area 30 comprises a flat portion201 provided in each non-connective area 34, a flat portion 202 providedin each connective area 33, and inclined portions 203 and 204 providedbetween flat portions 201 and 202. Flat portion 201, inclined portion203, flat portion 202 and inclined portion 204 are repeatedly formed inthis order in a second direction D2.

Flat portions 201 and 202 are parallel to, for example, the seconddirection D2. For example, inclined portions 203 and 204 are inclined atthe same angles as edges 41 and 42 of each branch area 40, respectively,with respect to a first direction D1. Projection portions 35 and concaveportions 36 are alternately formed in the second direction D2 by flatportions 201 and 202 and inclined portions 203 and 204. Each projectionportion 35 is a trapezoid comprising flat portion 201 and inclinedportions 203 and 204. Each concave portion 36 is a trapezoid comprisingflat portion 202 and inclined portions 203 and 204. Bend portions BP1and BP2 are formed at the borders between flat portion 201 and inclinedportions 203 and 204. For example, bend portions BP1 and BP2 areextensions of edges 41 and 42.

In the example of FIG. 9, the shape of each projection portion 35comprising inclined portions 203 and 204 and flat portion 201 is similarto that of each gap area 60 comprising edges 41 and 42 and a bottom edge31. In this disclosure, the term “similar” includes the meaning in whichtwo objects merely resemble each other in shape in addition to thegeometric meaning in which, when one of two objects is reduced orenlarged, the object coincides precisely with the other object. Forexample, even when the angle between each of inclined portions 203 and204 and flat portion 201 is different from the angle between each ofedges 41 and 42 and the bottom edge 31, the projection portion 35resembles the gap area 60 in shape in respect that they are trapezoidalas a whole. Thus, this case is included in the concept of “similar” inthe present disclosure.

Third Embodiment

FIG. 10 is a general plan view showing a part of a pixel electrode PEaccording to the third embodiment. In the pixel electrode PE shown inFIG. 10, an edge 32 provided in an axial area 30 comprises a curvedportion 301 provided in each non-connective area 34, and a flat portion302 provided in each connective area 33. The curved portion 301 and theflat portion 302 are repeatedly formed in a second direction D2.

For example, each curved portion 301 has an arcuate shape projecting toa second side SD2. Each flat portion 302 is parallel to, for example,the second direction D2. Projection portions 35 and concave portions 36are alternately formed in the second direction D2 by the curved portions301 and the flat portions 302. Bend portions BP1 and BP2 are formed atthe borders between the curved portion 301 and the flat portions 302.For example, bend portions BP1 and BP2 are extensions of edges 41 and42.

In the example of FIG. 10, each bottom edge 31 is curved in a mannersimilar to that of each curved portion 301. The end portion (bottom edge31) of each gap area 60 on the second side SD2 has an arcuate shapeprojecting to the second side SD2. A top edge 43 of each branch area 40has an arcuate shape projecting to a first side SD1.

In a manner similar to that of the second embodiment, the shape of eachprojection portion 35 including the curved portion 301 is similar tothat of each gap area 60 including the bottom edge 31. For example, evenwhen the curvature or the position of the center of curvature differsbetween each curved portion 301 and each bottom edge 31, each projectionportion 35 resembles each gap area 60 in shape in respect that they arecurved so as to project to the second side SD2 as a whole. Thus, thiscase is included in the concept of “similar” in the present disclosure.

Fourth Embodiment

FIG. 11 is a general plan view showing a part of a pixel electrode PEaccording to the fourth embodiment. In the pixel electrode PE shown inFIG. 11, an edge 32 provided in an axial area 30 comprises a curvedportion 401 provided in each non-connective area 34, and a curvedportion 402 provided in each connective area 33. Curved portions 401 and402 are repeatedly formed in a second direction D2.

Each curved portion 401 has an arcuate shape projecting to a second sideSD2. Each curved portion 402 has an arcuate shape depressed to a firstside SD1. Curved portions 401 and 402 are smoothly connected to eachother, and form a meandering shape. Projection portions 35 and concaveportions 36 are alternately formed in the second direction D2 by curvedportions 401 and 402. In the present embodiment, the borders betweencurved portions 401 and 402 are defined as bend portions BP1 and BP2.For example, bend portions BP1 and BP2 are extensions of edges 41 and42.

In a manner similar to that of the third embodiment, the shape of eachprojection portion 35 comprising curved portion 401 is similar to thatof each gap area 60 comprising a bottom edge 31.

Even with the shape of each pixel electrode PE of the second to fourthembodiments, when an electric field is generated between the pixelelectrode PE and the common electrode CE, the rotational directions ofthe liquid crystal molecules are aligned from the first edges 41 to bendportions BP2. Further, the rotational directions of the liquid crystalmolecules are aligned from the second edges 42 to bend portions PB1.Thus, in a manner similar to that of the first embodiment, the speed ofresponse in high-speed response mode can be further increased.

Fifth Embodiment

The fifth embodiment is explained. This section mainly looks at thedifferences from the first embodiment, and the explanations of the samestructures as those of the first embodiment are omitted unlessnecessary.

In the present embodiment, a common electrode CE is provided betweenpixel electrodes PE and a liquid crystal layer LC. In this respect, thepresent embodiment is different from the first embodiment. FIG. 12 showsa part of a cross-sectional surface of a display device 1 according tothe fifth embodiment. In a manner similar to that of FIG. 3, FIG. 12shows the cross-sectional surfaces of subpixels SPR, SPG and SPB in afirst direction D1. The illustration of scanning signal lines G or videosignal lines S is omitted. Further, each switching element SW issimplified.

In FIG. 12, the pixel electrodes PE are formed on a first insulatinglayer 11 and are covered with a second insulating layer 12. The commonelectrode CE is formed on the second insulating layer 12 and is coveredwith a first alignment film 13. The other structures are the same asthose of FIG. 3.

FIG. 13 is a general plan view of the common electrode CE. FIG. 13mainly shows a subpixel area A corresponding to a single subpixel SP. Inthe example of FIG. 13, the subpixel area A comprises a first area A1and a second area A2 in a manner similar to that of FIG. 4. The firstarea A1 comprises an axial area 30 and a plurality of branch areas 40.The second area A2 comprises a plurality of gap areas 60. In the presentembodiment, the first area A1 is an area in which the common electrodeCE is not present. The second area A2 is an area in which the commonelectrode CE is present. The first area A1 is a slit (aperture)comprising the axial area 30 and the branch areas 40. For the shape ofthe first area A1, any one of the shapes of the first areas A1 of thefirst to fourth embodiments may be applied. For example, in FIG. 13, thesame shape as that of the second embodiment (FIG. 9) is employed.

The pixel electrode PE has, for example, the outline indicated with thedashed frame, and overlaps the first area A1 as seen in plan view. Forexample, a light-shielding layer 22 overlaps the axial area 30 and theproximal and distal ends of each branch area 40, and opens in the formindicated with the alternate long and short dash line.

FIG. 14 is a partial enlarged view of the pixel electrode PE shown inFIG. 13. The axial area 30 comprises connective areas 33 andnon-connective areas 34 in a manner similar to that of the example ofFIG. 9. Each projection portion 35 is in alignment with a correspondinggap area 60 in the first direction D1. Each concave portion 36 is inalignment with a corresponding branch area 40 in the first direction D1.Further, the axial area 30 comprises the projection portion 35 in eachnon-connective area 34, and the concave portion 36 in each connectivearea 33. Bend portions BP1 and BP2 are formed at the borders between theconnective area 33 and the non-connective areas 34 (or the bordersbetween the projection portions 35 and the concave portion 36).

Even with this shape, in a manner similar to that of the aboveembodiments, the rotational directions of the liquid crystal moleculesare aligned from edges 41 and 42 of each branch area 40 to bend portionsBP1 and BP2. Thus, in the structure of the present embodiment, ahigh-response mode similar to that of the above embodiments can berealized.

Each of the first to fifth embodiments discloses a structure which canbe adopted when the dielectric anisotropy of the liquid crystalmolecules of the liquid crystal layer LC is positive. However, theliquid crystal layer LC may be structured by liquid crystal molecules inwhich the dielectric anisotropy is negative. In this case, the alignmenttreatment direction AD (or the initial alignment direction of liquidcrystal molecules) may be a direction (the second direction D2)perpendicular to the extension direction (the first direction D1) of thebranch areas 40.

All of the display devices which may be realized by a person of ordinaryskill in the art by appropriately changing the design based on thedisplay device explained as each embodiment of the present inventionfall within the scope of the present invention as long as they encompassthe spirit of the invention.

Various modification examples which may be conceived by a person ofordinary skill in the art in the scope of the idea of the presentinvention will also fall within the scope of the invention. For example,even if a person of ordinary skill in the art arbitrarily modifies theabove embodiments by adding or deleting a structural element or changingthe design of a structural element, or adding or omitting a step orchanging the condition of a step, all of the modifications fall withinthe scope of the present invention as long as they are in keeping withthe spirit of the invention.

Further, other effects which may be obtained from the embodiments andare self-explanatory from the descriptions of the specification or canbe arbitrarily conceived by a person of ordinary skill in the art areconsidered as the effects of the present invention as a matter ofcourse.

What is claimed is:
 1. A liquid crystal display device comprising: afirst substrate; a second substrate; a light-shielding layer; and aliquid crystal layer including liquid crystal molecules between thefirst substrate and the second substrate, wherein the first substratecomprises: a plurality of video signal lines; pixel electrodeselectrically connected to the video signal lines; a common electrodefacing the pixel electrodes and rotating the liquid crystal molecules bygenerating an electric field between the common electrode and the pixelelectrodes; and a plurality of subpixel areas each comprising a firstarea and a second area, the first area is an area in which the pixelelectrode is present, and the second area is an area in which the pixelelectrode is not present, each of the subpixel areas comprises a firstside and a second side in a first direction, the first area includes anaxial area extending in a second direction intersecting the firstdirection, and a plurality of branch areas extending in the firstdirection from the axial area to the first side, the second areaincludes a gap area extending in the first direction between theadjacent branch areas, and the axial area comprises a projection portionprojecting to the second side and in alignment with the gap area in thefirst direction, and overlaps the light-shielding layer.
 2. The liquidcrystal display device of claim 1, wherein the axial area includesconnective areas connected to the branch areas, and a non-connectivearea adjacent to the gap area, and a width of the non-connective area inthe first direction is less than or equal to one-fifth of a total widthof the connective area and the branch area in the first direction. 3.The liquid crystal display device of claim 2, wherein a width of thenon-connective area in the second direction is greater than a width ofthe connective area in the second direction.
 4. The liquid crystaldisplay device of claim 1, wherein each of the branch areas comprises afirst edge and a second edge arranged in the second direction, and whenthe electric field is generated, a rotational direction of the liquidcrystal molecules differs between a vicinity of the first edge and avicinity of the second edge.
 5. The liquid crystal display device ofclaim 1, wherein an end portion of the gap area on the second sideprojects to the second side.
 6. The liquid crystal display device ofclaim 1, wherein the axial area includes connective areas connected tothe branch areas, and a non-connective area adjacent to the gap area,and the axial area comprises a bend portion in an edge on the secondside at a border between the non-connective area and the connectivearea.
 7. The liquid crystal display device of claim 1, wherein the axialarea includes connective areas connected to the branch areas, and anon-connective area adjacent to the gap area, and a length of theprojection portion in the first direction is greater than or equal toone-third of a length of the non-connective area in the first direction.8. The liquid crystal display device of claim 1, wherein the firstsubstrate comprises a first alignment film, the second substratecomprises a second alignment film, and an alignment direction of theliquid crystal molecules by the first alignment film and the secondalignment film conforms to the first direction or a directionperpendicular to the first direction.
 9. The liquid crystal displaydevice of claim 1, wherein the first substrate comprises a firstalignment film, the second substrate comprises a second alignment film,and at least one of the first alignment film and the second alignmentfilm is an optical alignment film.
 10. The liquid crystal display deviceof claim 1, wherein each of the branch areas comprises a first edge anda second edge arranged in the second direction, the axial area includesconnective areas connected to the branch areas, and a non-connectivearea adjacent to the gap area, the axial area comprises a bend portionin an edge on the second side at a border between the non-connectivearea and the connective area, and when the electric field is generated,the liquid crystal molecules rotate in a first rotational direction froma vicinity of the first edge to a vicinity of the bend portion which isan extension of the first edge, and the liquid crystal molecules rotatein a second rotational direction different from the first rotationaldirection from a vicinity of the second edge to a vicinity of the bendportion which is an extension of the second edge.